St. Bartholomew's Church is one of the oldest church buildings in Ljubljana. The church was first mentioned in 1370, when in front of it a peace treaty between the Doge of Venice and Leopold III and Albert III of Habsburg was concluded by their representatives on 30 October 1370, in which the Austrians agreed to return the city of Trieste for the compensation of 75,000 florins.
In 1526, its valuables were donated to a fund for improving the city's defenses against Turkish attacks. In the end of 15th century and beginning of 16th, it was a venue of Protestant liturgy and was during Slovene anti-reformation in 1618, it was reclaimed as a Roman Catholic church. In 1825, it was damaged by fire and restored several times.
Some elements of the original Romanesque church have been preserved, among them the portal on the northern side. Between 1933-36, the church was partially redesigned according to plans by Jože Plečnik.
References:The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.